Epitaxial Ge growth on Si(001) substrates and in-situ doping using UHV-CVD

Summary form only given. Monolithic integration of photonic devices with electronics has attracted interest and there has been growing interest in photonic devices based on Si-compatible materials. Ge has a bandgap of 0.67 eV at room temperature and high absorption coefficient in the range of 1.3 - 1.55 μm. Furthermore, when biaxial tensile stress is applied to Ge, it transforms from an indirect to a direct bandgap material and optical properties are improved. Such properties of Ge enable the application to the optoelectronic devices such as an emitter and a detector. Ge epitaxial growth on a Si substrate is a promising technology because it can induce thermal tensile strain in Ge and make possible to integrate Ge optical devices on Si CMOS platform. In order to adapt Ge epitaxial layers on devices, the great challenge is the lattice mismatch of 4.2% between Ge and Si. This mismatch causes rough surface with island formation which hinder the device process and generates a high density of threading dislocations on the order of 10<;sup>8<;/sup> cm<;sup>-2<;/sup> which act as non-radiative recombination centers, degrading the performance of Ge devices. To overcome such limits, two-step Ge growth has been suggested which uses Ge layers grown at low temperature(LT). In two-step growth, the LT Ge works as a buffer layer which provides nucleation sites for misfit dislocation and inhibits the propagation of threading dislocation by generating point defects. Thus, the optimized buffer layer is needed to grow high quality Ge epitaxial layer on Si. Furthermore, in-situ doping of Ge is desirable due to the potential to form p-n junction without any ion implantation damage. In this study, we investigated the growth conditions for the two-step Ge growth and in-situ boron doping was proceeded.